It can also be seen that the intersection of UF and UB mainly appeared before 1999, after which both CCDI values and UF and UB showed a clear trend of increasing drought.
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Analysis of the spatial and temporal evolution of drought in Henan based on a nonlinear composite drought index.
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The sentences
Overall, the linear propensity of CCDI at the monthly, quarterly and annual scales were -0.003-10a-1, -0.0013-10a-1, and -0.0105-10a-1, respectively, and all of them showed a decreasing trend.
12 d) CCDI showed a decreasing trend at a rate of − 0.0115·10a −1 , − 0.0049·10a −1 , and − 0.0077·10a −1 , respectively, and an increasing trend at a rate of 0.0064·10a −1 in winter (Fig. 12 d).
In this study, we found that the comprehensive drought index had an increasing trend of drought in Henan at the monthly, seasonal and annual scales, and the annual scale had an obvious trend of drought higher than the seasonal and monthly scales, which is the same as Dang Luo’s 63 analysis of meteorological drought in Henan with SPEI pointed out that the trend of drought increase at the annual scale was obviously higher than that at the seasonal and monthly scales, and Li Y 64 pointed out that agricultural drought in Henan had an increasing trend at the seasonal and annual scales with the use of TVDI, which is the same as this study’s analysis at the seasonal and annual scales.